Take an average record. A groove cut into the surface of the vinyl contains music. For a standard LP, the groove is 1,500 feet long.

The groove is the physical embodiment of music. And one type of music history would emphasize how the manufacturing of these discs -- and their interplay with the technologies of radio -- shaped what people listen to, what people consider "normal" in music. The short length of playable music that could be encoded on a 45 (and the older 78 technology) influenced what could be sold, which influenced radio play, and helped determine the standard length of a song.

Pop musicians playing with the limits of 45s began to make longer art during the 1960s, exploiting the 50 minutes or so of music that the 1,500 feet of groove allowed. This, in turn, precipitated change in the music discovery medium of the day (radio) and on it went.

I can remember the first album I had on vinyl. I was maybe five years old, and my sister gave me the Top Gun soundtrack. Dancing on the carpet of the living room in Sylmar, California. I can't even remember how I must have moved. How do you dance to "Highway to the Danger Zone"? I did, though. I did.

My dad had CDs by the late 80s. Their rainbow reflections seemed like a mirror from the future. He owned mostly classical music and, as I recall, U2's Joshua Tree. I remember listening to that album together, clustered around the stereo, which he kept in a large cabinet with a plastic door. By the time we left Los Angeles in 1992, I had even acquired a CD. I'm pretty sure it was 4 Non Blondes' Bigger, Better, Faster, More!. I tried to sing the hit single, "What's Up?" but my voice was already changing.

Every physical medium had its little quirks. Recall: most tape players couldn't skip tracks. But it was easy to record on tapes. Meanwhile, it was a revelation when CD players could loop individual tracks or the whole disc at the touch of a button. But man, did they skip with the early portable players. And the read-write capability was lost for most systems. You could burn CDs from your computer, but no one recorded the radio onto CDs like they did with tapes.

We expect this kind of thing to influence the way we experience, maybe even hear, music. But what about the digital interfaces that now dominate the market? Shouldn't they exert just as much of an influence over how we listen and how artists create?

For me, all that began in 1994, when we got the Internet. And it must have been a couple years later that I started downloading MP3s from FTP sites over our impossibly slow dial-up connection. The first was almost certainly "No Diggity" by Blackstreet, so it must have been 1996. A few years later, Bain says that global music sales peaked.

I do not approve of this remix, but it exists.

With the full speed of collegiate broadband at my back, I got into the obscure music sharing site Soulseek, and like everyone else at school, developed an huge library of music that I hadn't paid for. I traded mix albums with friends. I got my first MP3 player. I got an iPod.

At a handwaving/fan level, it's easy to say that the iPod encouraged ownership. That little hard drive was your record crate, your folder full of CDs, and your wall of music posters in one. And it was *all* your music, which made it meaningful. A common practice was to just 'shuffle' the whole thing, letting the iPod -- not a recording artist -- select your next track.

iTunes provided a big market for singles for the first time in decades, and made playlists easy, too. The units that really seemed to matter were the single song and the totality of the collection.

All the new things have antecedents in the old things: the CD purchases, broadcast radio stations, the mix tapes, and the free-for-all of Napster-style music piracy. But the fact that there are continuities do not mean that nothing has changed. Streaming music services like Pandora encouraged a different kind of behavior all together. They were personalized radio, and they put the full-weight of whizbang algorithmtude behind their track selections. In the early days, they heavily promoted the Music Genome Project, which claimed to be able to break music into its components to find what you liked deep inside the music, and then serve up novel recombinations of those sound structures. Your results varied, but it was interesting. If the iPod collection was the phenotype, Pandora claimed to find the genotype. Personal genomics for your taste. 23andMe for people who like The Monkees.

Pandora never quite sat right with me, though. I felt like it never quite understood me. Like, just because I like soul music from Philadelphia in the early 1960s doesn't mean that I like late-1980s, peak-synth Quincy Jones. On the other hand, it was cheap and discovering new music was fun.

Rdio's office in San Francisco (Alexis Madrigal)

In 2010, I got Rdio. I liked it because, in contrast to Spotify, it struck me as admirably traditionalist about music. Even though you could find out about music from what your friends were listening to, the service hewed closely to the old LP interface. Rdio's user interface was organized around albums, and looking through the site felt like browsing the racks at a record store. It was a happy medium between the anarchic glee of music piracy, the iTunes pay-per-song model, and the pure streaming models like Pandora. Rdio, for me, is a huge record store that I can shop in as much as I want to for $10 a month. Rdio VP of product Chris Becherer called it "the celestial jukebox." It completely changed my music habits. I listen almost exclusively to Rdio, while my (lovingly collected) MP3 collection sits on a hard drive somewhere in a closet. But I wonder: how is it warping my ears?

All this to say: music distribution is crazy these days. On one axis, there are competing business models: transactional ones like iTunes, in which you pay per song/album versus access models like Rdio/Spotify/Pandora, where you pay a monthly fee for the ability to play a library of music. On the other axis, there are new possibilities in music listening. Music fans can stick with albums or singles (the units of yore), create their own playlists, or stream computer-generated playlists of all kinds.

The classic behaviors of discovery, acquisition, and consumption are all being extended and mutated and monetized.

And things got a lot muddier this week when Rdio amped up its Pandora-like Stations offering. Now, you can pick an artist, label, or friend, and stream a playlist of music based on them. Tracks are selected by a heavily modified version of EchoNest's recommendation algorithm going to town on Rdio's collection of 20 million songs (Pandora has about a million). Rdio doesn't disclose how many free or subscribing users it has, but, by all accounts, it is much smaller than Pandora, which has more than 70 million users.

Previously, the Rdio interface allowed four types of browsing. First, there is Heavy Rotation, which algorithmically spits out album recommendations based on what your friends on the service are listening to. Then you could look at Recent Activity, which showed what individual friends were up to. Then there were the general Top Charts and New Releases. Stations, streaming music based on artists, labels, or friends' listening habits, have now been promoted to join them.

It might sound like a small change. It is. But it's the first time Rdio has de-emphasized album-based listening. Outgoing CEO Drew Larner told me that it was part of the service's attempt to be your "one-stop shop," though he maintained that their "core notion of social discovery is never going to go away."

The New Releases tab on Rdio changed my life. For the first time in six or seven years, I found myself waking up on Tuesdays and practically running to the computer. At dinner, I'd play new music for my wife. The Recent Activity tab helped me peek in on what my father was listening to, and suddenly, we had a whole new conversational terrain to explore. A sampling of his recent selections: The Best of Caetano Veloso, the Alabama Shakes Station, The Rolling Stones' Flowers, Macklemore & Ryan Lewis, Ennio Morricone's greatest hits, and the 38-CD Karajan Symphony Edition.

Rdio has always been known as a design-centric product since Wilson Miner was at the helm. Current head of design Ryan Sims continues that tradition with the framing of the Stations feature. The background is formed by taking the cover of the album playing, blowing it up, and blurring it out. It looks beautiful. The current, previous, and next album covers sit on the blur. Above them, five radio buttons range from Familiar to Adventurous. (I love that they used the word "adventurous." It's the perfect word there.) As the albums play, they move from right to left; in Rdio, horizontal scrolling indicates that the music will play forever. The whole experience is simple and slick.

It also happens to already be where Apple's new mobile operating system, iOS 7, is going. It's flat, which is to say, it doesn't have 3D effects. It's got the soft blur going, which is a new Apple design trope. And, on mobile, they make use of the z-axis; you can stack different types of action screens on one another, and then swipe them away when you're done with them.

Like Stations, the design of the new mobile app for Rdio also emphasizes listening. While Rdio has long had a collector component, as they try to mainstream their app, Sims decided to push collecting and sharing "to the back." In practice, this literally means that when you are listening to a song and want to add it to your collection, you have to long-press the album to bring up the menu you need. It was a small concession, Sims thinks, for the feeling that all "the music is waiting there to be tapped."

Sims, by the way, got his start designing interactive products by creating a Mandy Moore skin for the old, glorious MP3 player WinAmp, which was most popular in the late 90s and early 2000s as I was amassing my MP3 collection. That's the sort of thing we did when we were kids, and it shaped our expectation of how music should work now.

Meanwhile, KIDS THESE DAYS the music consumers of the future are forming a completely novel set of habits. My completely unscientific survey of people under the age of 22 finds that perhaps *the* dominant way they listen to music is via playlists on YouTube. Others seem drawn to the new singles and remixes on Soundcloud or Audiomack, or the Tumblr posts about singles and remixes, at least.

Whatever it is that they're doing, they're not even developing the basics of music purchasing, like thinking of the album as the basic unit of music. For them, it's the embed. For them, all "the music is waiting there to be tapped."

For artists, this attitude may not be a good thing. I spoke with Ryan Lamb of Alpine, a Melbourne rock band that's taken off on Rdio, about how streaming music services work for the producers. Lamb said their exposure on Rdio got their name out in the US, where they were not as well known as back home in Australia. Before their marketing hit the US, they had 150,000 plays. "It went crazy out of nowhere," he said. "It was definitely the most organic growth we've had on anything. But at the end of the day, as with YouTube and SoundCloud, it's basically just marketing."

"I'm sure there is some money in there. But we haven't seen it," he said. "We just think of it as marketing. It's another tool in the same way that YouTube is. Four million plays on YouTube doesn't mean anything unless you can get people to the shows."

All these little grooves that designers bake into an interface to make it harder or easier to do something: they are changing the way we listen to music, I'm sure of it. But it's hard to know exactly how. I asked Rdio for stats that might show how their listeners' habits are different from those of other services or even people who still listen just to CDs. Like: how do Rdio's top albums differ from the overall Soundscan numbers, and is it the nature of the tool or the nature of the audience?

But it's hard to get good data. All we've got is intuition to go on.

"This is pure speculation," Laurie Dewan, VP of Monetization, told me. "But the way I envision it in my mind is that [Rdio musical discoveries] are much spikier. You have these edges all around. The way that the music takes them to the next thing is so much richer. They have 8 ways to get to the next song."

Imagine any given music. For me, I've been listening to a ton of the Colombian salsa group Fruko y Sus Tesos, but specifically tracks from the 1970s on the Discos Fuentes label. I once played the Disco Fuentes station, which led me to hear the song "Periódico de Ayer" as performed by Hector Lavoe, which then led me to the oeuvre of the song's composer, Curet Alonso.

It's not that you couldn't or wouldn't take a similar jag in the physical media world or the MP3 days. I remember something like it with the Jamaican label Studio One jumping off from the Leroy Sibbles' cover of "Groove Me." But it would either A) take weeks, and cost hundreds of dollars or B) be completely self-directed and require a ton of scouring around for information to take a similar course through musical history.

Rdio -- especially now -- makes it so, so easy to find music you love, hopping from one act to the next.

I fire up Alexis FM, as Rdio calls my station, and crank it all the way to max adventurousness. Up first comes The Rolling Stones' "Paint It Black," which is a great song that reminds me of a bouncy French cover I heard one time. I Google around and discover it's called "Marie Douceur Marie Colere" and was performed by Marie Laforet. It is so good.

I fire up the station for that song, skip past some Brigette Bardot, and land on Nino Ferrer's "Le Telefon." But eventually that station devolves into the kind of pan-European vocal music you hear at bad Italian restaurants. I switch back to Alexis FM, and am rewarded with first Blue Oyster Cult's "Stairway to the Stars," and then a deep Hendrix cut, "If 6 Was 9."

And suddenly, I'm back in the 7th grade, holding on to my new CD, the Jimi Hendrix Experience. I have just heard "All Along the Watchtower" for the first time, blasting through the speakers of our Mercury Sable station wagon. It's a Bob Dylan cover, someone told me. And I can remember thinking, "Who's Bob Dylan?" Bob Dylan's artist station serves up "Subterranean Homesick Blues."

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